PURPOSE: To eliminate a break in a dislocation preventing part while preventing a hook part from easily coming off even when abnormal external force is applied to the hook part to a bracket.

CONSTITUTION: A V-shaped fold-back part 2c is formed in the point end of a hook part 2 of a tension spring 1 where a wire rod is helically wound. The fold-back part 2c is elastically deformed and inserted through a hole 3a of a bracket 3. The fold-back part 2c, inserted through the hole 3a, is restored by elastic force, to prevent the hook part 2 from coming off.